1. Field of the Invention
The present invention relates to an ink jet print apparatus, an ink jet print method and a program for forming an image on a print medium by ejecting ink from a print head according to print data.
2. Descrption of the Related Art
Office automation equipment such as personal computers and word processors are in wide use today. A variety of printing apparatus and methods have been developed to record information output from these office equipment on various print media. There is a growing trend in office equipment for displaying video in color thanks to their improved processing capacity. In line with this trend, more and more printing apparatus capable of recording information in color are being developed.
Printing apparatus capable of forming a color image vary widely in price and function, ranging from low-cost devices with relatively simple functions to multifunctional ones that let user to select a desired print speed and quality according to the kind of an image to be printed and to its use. An ink jet printing apparatus in particular has found a wide use, such as on printers, copying machines and facsimiles, because of its many features including low noise, low running cost, small size, and relative ease with which a color image can be formed.
Generally, a color ink jet printing apparatus forms a color image using three color inks, cyan, magenta and yellow, or four color inks further including a black ink. Many of them use an aqueous liquid containing a coloring material. Thus, for an ink to soak into a print medium and dry there takes a certain length of time. Therefore, not many printing apparatus have been available which can perform a high-speed printing. Now that a variety of uses have been emerging as described above, there is a growing demand for a faster printing speed. In recent years high-speed printing apparatus are on the market which can print more than five, or even 10, A4-size sheets a minute.
Home-use ink jet printing apparatus are rapidly proliferating which can print a user-designed image including photograph on a large number of New Year postcards continuously. A printing apparatus is also reaching the market which can realize a so-called “full bleed printing” by which an image is printed to the edges of a print medium.
When a large number of postcards are to be printed, a normal process is as follows. First, only an address side or a message side (where a photograph or message is to be printed) of one or more cards is printed; and then the user turns over these cards and feeds them into the printing apparatus for printing on their opposite side. This procedure is troublesome for the user and there is a possibility of the user inserting the cards in a wrong direction. To deal with this problem, a printing apparatus has already been proposed which, as disclosed in Japanese Patent Application Laid-open No. 2000-191204, has an automatic reversing unit for automatically turning over sheets.
In the printing apparatus incorporating the automatic reversing unit, one side of the print medium is first subjected to an ordinary printing, after which the print medium is pulled back in the opposite direction to the automatic reversing unit installed in the printing apparatus. Upon receiving the print medium, the automatic reversing unit turns it over so that its unprinted side faces the printing unit then the print medium is transported from the automatic reversing unit to the printing unit. The printing unit prints on the unprinted side of the reversed print medium, which is then discharged from the printing apparatus. With the above steps automatically executed, the address side and the message side of a postcard can be printed in one process.
In the ink jet printing apparatus that performs the automatic double-sided printing, however, problems may arise during the transport process. They are explained as follows.
One of the problems is a curl of a print medium. Since the ink jet printing apparatus generally uses aqueous inks, after plain paper or ink jet paper absorbs inks, paper fibers may contract curling the paper. Particularly when the above “full bleed printing” is performed or when a small-sized postcard is printed with a plurality of color inks and therefore with a large volume of inks, the print medium absorbs inks up to its edge, which makes the curl phenomenon more conspicuous. If the double-sided printing is performed on the curled postcard, when the postcard is transported for the double-sided printing, ends of the card may be caught on parts of the automatic reversing unit or printing apparatus body, making it impossible for the card to be fed smoothly into the printing apparatus or the printing unit.
Further, since a fixing time of ink varies depending on the type of print medium and ink used and on ambient temperature and humidity, another problem arises from a failure to completely manage these factors.
In addition to printing high-quality photographic images on New Year greeting cards as described above, the user often prints simple documents and Internet web pages on plain paper on a daily basis. Actually, an appropriate kind of ink to be applied varies according to the use. In printing a high-quality photographic image, it is generally considered advantageous to use an ink composed mainly of a dye-based colorant with an excellent penetrability (hereinafter referred to as a penetrative ink). However, the penetrative ink is generally not vivid when printed on plain paper and thus not so suited to printing simple documents on plain paper on a daily basis. In contrast to this, ink capable of realizing a high-quality printing even on inexpensive plain paper is said to be an overlay type ink that contains such a colorant as pigment. Unlike the penetrative ink, the overlay type ink, when it uses a pigment as colorant, has larger colorant particles than a dye ink and thus cannot easily penetrate deep into fibers of the print medium, with the result that the colorant particles are more likely to stay on a surface layer of the print medium. Therefore, output images printed with the overlay type ink have a higher optical density than those printed with the penetrative ink. Further, since an ink penetration (spread) to the surrounding area is also smaller than when the penetrative ink is used, image boundaries are clearly printed. On the downside, since the colorant stays and becomes fixed near the surface layer of the print medium, the printed surface tends to be rough. This means it has a lower rubbing resistance than the penetrative ink. The degraded rubbing resistance gives rise to another problem that ink can easily come off even with a slight friction. Another drawback of the overlay type ink is a longer fixing time required than that of the penetrative ink.
To make the most of the features of these inks, an ink jet printing apparatus has been proposed which uses both of the penetrative ink and the overlay type ink (or dye ink and pigment ink). Such an ink jet printing apparatus often uses a pigment-based overlay type ink for only a black ink that is most consumed in document printing and dye-based penetrative inks for color inks (cyan, magenta and yellow inks including those of differing densities).
In such an ink jet printing apparatus incorporating inks with different features, when the above double-sided printing is performed, the ink fixing time for the first side of the print medium that is printed first varies depending on which ink is applied. If the print medium with the ink on the first side not yet fully dry is transported to the automatic reversing unit and turned over, the printed surface on which the ink is not yet fully fixed may directly come into contact with, and be rubbed by, inner mechanisms of the apparatus, causing many problems including a significant degradation of the print quality or a smearing of the inner mechanisms with ink. This in turn may lead to another problem of a secondary smear, in which the next print medium will be smeared by the contaminated inner mechanisms. Although the ink kind is taken as an example, the above problem similarly arises depending on the type of print medium used, ambient humidity and temperature.
As described above, the conventional printing apparatus with an automatic double-sided printing function cannot avoid a variety of problems completely. That is, depending on the type of print medium, the kind of ink and whether the “full bleed printing” is executed, the quality of a printed image formed by the automatic double-sided printing varies and the inner mechanisms of the printing apparatus are smeared. To cope with this situation, many of the currently available ink jet printing apparatus capable of automatic double-sided printing are constructed to allow a selection between a conventional, manual double-sided printing process and an automatic double-sided printing process using the automatic reversing unit. Thus, in performing the double-sided printing, the user must consider various conditions and decide which printing process, manual or automatic, should be used. That is, the conventional problems, including troublesome steps and a possibility of erroneous insertion on the part of the user, are not avoided completely.